1. Field of the Invention
This invention relates to optical transducers, and more particularly to optical transducers for determining position, orientation, direction, revolution, acceleration, fluid flow, fluid level, torque, pressure, opacity, and the like.
2. Description of the Related Art
Transducers for determining linear or angular position along one or more axes, orientation, direction, revolution, acceleration, fluid flow, fluid level, torque, pressure, and the like, are often used in vehicles, industrial equipment and other systems and components. Such transducers typically operate by detecting a change in an electrical property of the transducer, such as a change in resistance, capacitance, current flow, magnetic field, and so on, and may be embodied by variable capacitor or resistor mechanisms, optical systems, or Hall effect sensors.
By way of example, prior art liquid level sensors, such as fuel sensors for motor vehicles, usually include a float that rides on an upper surface of the fuel in a fuel tank. The float is typically connected to one end of a pivot arm while the other end of the pivot arm typically includes a wiper mechanism that brushes against a resistor strip when the arm is rotated due to a change in fuel level in the tank. Such sensors are prone to wear, mechanical and/or electrical breakdown or, at the very least, inaccurate liquid level detection. Although variable capacitance probes have been developed to overcome these drawbacks, they are cost-prohibitive in many applications and are typically limited to measure a certain type of liquid, since different liquids will have different dielectric properties. For example, a variable capacitance probe designed to measure fuel level normally will not be designed to measure water level.
Prior art linear transducers, such as linear variable differential transformers (LVDT's), are commonly used to detect the relative linear movement between objects, such as relative movement between a movable machine element or assembly and a stationary machine support. Although these transducers work well for their intended function, they are relatively heavy, difficult to manufacture, and high in cost, making them impractical for many low-cost applications.
Prior art angular position transducers and rotary sensors typically include a transparent encoder disk and a circumferential track imprinted thereon. A light source is positioned on one side of the disk in alignment with the track and a pair of spaced photodetectors are positioned opposite the light source on the other side of the disk. Typically, each track comprises a series of equally-spaced opaque bars separated by transparent sections. As the disk rotates, the bars and transparent sections cause the photodetectors to alternate between high and low states. A microprocessor typically receives the high and low states of each photodetector and determines the direction of disk rotation depending on which photodetector goes high or low first. The number of high or low states are then added or subtracted (depending on the direction of disk rotation) in order to determine the angular position of the encoder disk. These types of transducers can be relatively difficult and costly to manufacture and their resolution is typically limited by the number of bars in the circumferential track, the spacing between bars, the relative size of the transducers, and other factors. The bars must be accurately positioned on the disk, and the light source and photodetectors must be positioned very accurately with respect to the bars so that direction of disk rotation can be ascertained.